1. Field of the Invention
The present invention relates to a fixture structure, an optical device having the fixture structure and used in a copier, an image scanner, or a facsimile machine; and to an image reading device, and an image forming device.
2. Description of the Related Art
In the related art, in an optical device such as an image reading device used in a copier, an image scanner, or a facsimile machine, the constituent components of the optical device are fixed by using screws. For example, such optical devices are described in Japanese Laid-Open Patent Application No. 2001-313779 (below, referred to as “reference 1”), Japanese Laid-Open Patent Application No. 2002-311364 (below, referred to as “reference 2”), Japanese Laid-Open Patent Application No. 11-227249 (below, referred to as “reference 3”), Japanese Patent Gazette No. 2794892 (below, referred to as “reference 4”), Japanese Laid-Open Patent Application No. 2000-193863 (below, referred to as “reference 5”), and Japanese Laid-Open Patent Application No. 5-297256 (below, referred to as “reference 6”).
In the image reading device, it is required that pixels of a photoelectric conversion element thereof, such as a CCD, be smaller and smaller, and the number of the CCD pixels be more and more. In order to achieve a large number of small CCD pixels, it is necessary to reduce the magnification of a lens for forming a reflection image of the original image on the CCD, and it is necessary to increase position precision between the constituent components of the image reading device.
For example, consider an image reading device for reading a document of A3 size at 600 dpi; if pixel intervals of the CCD are 10 μm, it is required that the magnification of the lens be 0.24; if the pixel intervals of the CCD are 5 μm, it is required that the magnification of the lens be 0.12. On the other hand, since the required position precision of the lens and the CCD in the optical axis direction relates to the square of the pixel intervals, if the pixel intervals are reduced by half, it is required that the position precision be improved by four times.
In other words, when an image reading device has CCD pixel intervals of 5 μm, in order to obtain the same image quality as an image reading device having CCD pixel intervals of 10 μm, it is required that the relative position precision of the constituent components of the image reading device be improved by four times. For example, if the position precision of the constituent components in the image reading device having CCD pixel intervals of 10 μm is 20 μm, the position precision of the constituent components in the image reading device having CCD pixel intervals of 5 μm should be 5 μm.
As described in reference 1, it is known that the position precision of the constituent components attached with screws is from several hundreds μm to several tens μm Due to this, although a high position precision of the constituent components is required when the CCD pixel intervals are reduced, it is difficult to obtain the required position precision by attaching the constituent components of the optical device with screws.
To meet this requirement, so far one usually slowly fastens the screws while confirming the optical property. Specifically, each time a screw is fastened, the optical property is confirmed; if the optical property does not meet the required level, the screw is unfastened, the relative position precision of the constituent components is adjusted, then the screw is fastened again, and then the optical property is confirmed again. As a result, it takes a long time to attach the components; hence, assembling the image reading device is quite time-consuming, and productivity of manufacturing the image reading device is low.
In addition, while the screws are being fastened, positions of the constituent components of the optical device may shift. When adjusting the positions of two components and fastening the screws, usually, one component is fixed, and the other component is fastened with positioning means, such as a chuck. Then, the relative position of the two components is adjusted with the positioning means, and the screw is fastened after the position adjustment. Then, the chuck on the other component is unfastened to finish fastening the two components.
In the above process, since the positions of the two components are adjusted while the other component is fixed with the chuck, the other component receives a force from the screw when the screw is fastened on the other component, and a force from the chuck. Thus, when the chuck on the other component is unfastened, the other component only receives a force from the screw when the screw is fastened, and this force may change the position of the other component determined through the position adjustment.
In addition, if the position adjustment of the two components is performed with the screws being unfastened, and the two components are fixed after the screws are fastened, since the two components change from a free state, in which the two components are freely movable relative to each other, to a fixed state, in which the two components are fixed relative to each other, the relative position of the two components changes before and after the screws are fastened. In order to reduce the change of the relative position, it is necessary to adjust the relative position of the two components while the screws are being sufficiently strongly fastened so as to reduce the difference of the fastening power of the screw between the free state, in which the two components are freely movable relative to each other, to the fixed state, in which the two components are fixed relative to each other. However, it is apparent that a strong force is required to move the two components relative to each other when the screw is fastened strongly.
Due to this, in order to easily move the two components relative to each other with the screw being fastened sufficiently strongly, usually, a notch is formed in communication with both of the two components, and a driver or another tool can be inserted into the notch to move the two components for position adjustment.
However, when inserting a tool into the notch, which is formed in both of the components, to adjust the relative position of the two components, sometimes the tool inserted into the notch may touch one of the two components unexpectedly. Especially, when the position adjustment of one of the two components has been finished, that is, the movement of the one component is restricted, if the tool touches the other component, the other component may move in an unexpected direction. Especially, the other component may move in the direction intersecting the direction in which the relative position of the two components is adjusted with the tool inserted into the notch. In this case, it is necessary to adjust the relative position of the two components in the direction in which the other component moves (that is, the unexpected direction); hence, it takes a long time to adjust the relative position of the two components.